The invention relates generally to a control system for operating condenser fans.
Certain refrigeration and air conditioning systems generally rely on a chiller to reduce the temperature of a process fluid, such as water, to produce chilled process fluid. Air may pass over the chilled process fluid in an air handler and circulate throughout a building or other application to be cooled. In typical chillers, the process fluid is cooled by an evaporator that absorbs heat from the process fluid by evaporating refrigerant within the evaporator. The refrigerant may then be compressed in a compressor and transferred to a condenser, such as an air cooled condenser. In an air cooled condenser, the refrigerant is cooled by air and condensed into a liquid. Air cooled condensers typically include a condenser coil and a fan that induces airflow over the coil. The amount of airflow over the coil may be varied by either adjusting the speed of the fan, or in multiple fan configurations, by staging the fans. Staging involves selectively operating fans associated with certain condenser coils. A combination of staging and varying fan speed may also be employed.
The amount of airflow over the condenser coils affects chiller efficiency. If the airflow is too high, the power necessary to create this excess flow represents wasted energy. If the airflow is too low, the compressor may have to expend extra energy to provide sufficient cooling. Prior attempts have been made to optimize airflow over condenser coils. For example, some chillers compute desired airflow based on ambient temperature. However, optimal airflow is independent of ambient temperature. Therefore, chillers that implement airflow control based on this parameter may not be operating at maximum efficiency. Similarly, chillers that adjust airflow based on condenser pressure also may operate at reduced efficiency. Running a chiller at lower efficiency results in higher operating costs.